Bis(Fluoroalkylsulfonyl)imides, (fluoroalkylsulfonyl)(fluorosulfonyl)imides and derivatives thereof are known to be useful in many chemical processes and formulations. In solution, the imides behave as strong acids due to the presence of the electron-withdrawing fluoroalkylsulfonyl or fluorosulfonyl groups and exhibit exceptional stability under a variety of conditions. These compounds have been found to be useful, for example, as fuel cell electrolytes, as esterification catalysts and as polymerization catalysts for cationically-sensitive monomers such as epoxy resins.
The salts of bis(fluoroalkylsulfonyl)imides and (fluoroalkylsulfonyl)(fluorosulfonyl)imides have been found useful as electrolytes in advanced high voltage batteries. In particular, lithium bis(trifluoromethylsulfonyl)imide (CF.sub.3 SO.sub.2).sub.2 N.sup.- Li.sup.+, shows excellent conductivity and stability, but can be corrosive toward aluminum. Certain higher homologues of this compound show comparable performance as battery electrolytes, and have decreased the corrosion toward aluminum.
There are several known methods for preparing some classes of bis(fluoroalkylsulfonyl)imides. Bis(perfluoroalkylsulfonyl)imides can be prepared by the reaction of an alkali metal salt of an N-trimethylsilyl perfluoroalkylsulfonamide with a perfluoroalkylsulfonyl fluoride in a polar organic solvent. This route requires several synthetic steps, with the isolation of intermediate compounds, and the overall yields are often low. A second method involves the reaction of an alkali metal salts of a perfluoroalkylsulfonamide with perfluoroalkylsulfonyl fluoride in a polar organic solvent. Here too, the yields are low. A third method involves reacting a perfluorinated sulfonic anhydride with urea and a sulfonic acid. The products of this reaction are then dissolved in water and the addition of tetrabutylammonium bromide precipitates the tetrabutylammonium imide. This method is not satisfactory for the large scale production of imides because the overall yields are low and the sulfonic anhydride precursors are not easily accessible. A fourth method of making metal salts of sulfonimides involves the reaction of a metal nitride with perfluoroalkyl sulfonyl halide. However this method cannot be used to make unsymmetrical imides and requires handling metal nitrides which are sensitive to air.
Thus there remains a need for an efficient method of preparing bis(fluoroalkylsulfonyl)imides, (fluoroalkylsulfonyl)(fluorosulfonyl)imides, and derivatives thereof.